1. Field of the Invention
The present invention relates to a semiconductor device and its manufacturing method, and more particularly, to a diode such as a Schottky barrier diode (SBD), a tunnel diode and a PIN diode and its manufacturing method.
2. Description of the Related Art
A first prior art Schottky barrier diode is of a lateral type which is constructed by a semi-insulating GaAs substrate, an nxe2x88x92 -type GaAs contact layer formed on the GaAs substrate, an n+ -type GaAs layer formed on the nxe2x88x92 -type GaAs contact layer, an anode electrode (Schottky electrode) formed on the nxe2x88x92 -type GaAs contact layer, and a cathode electrode (ohmic electrode) formed on the n+ -type GaAs layer. This will be explained later in detail.
In the above-described first prior art Schottky barrier diode, however, since the path of the current adjacent to the surface of the nxe2x88x92 -type GaAs contact layer is relatively long and, is also very close thereto, the current is affected strongly by a surface level of the nxe2x88x92 -type GaAs contact layer. As a result, the low frequency noise characteristics such as 1/f noise of the Schottky barrier diode remarkably deteriorates.
A second prior art Schottky barrier diode is of a vertical type which is constructed by a semi-insulating GaAs substrate, an n+ -type GaAs contact layer formed on the GaAs substrate, an nxe2x88x92 -type GaAs layer formed on the n+ -type GaAs layer, an anode electrode (Schottky electrode) formed on the nxe2x88x92 -type GaAs layer 203, and a cathode electrode (ohmic electrode) formed on the n+ -type GaAs contact layer (see JP-A-8-255838). This also will be explained later in detail.
Thus, in the above-described second prior art Schottky barrier diode, the path of the current adjacent to the surface of the n+ -type GaAs contact layer is shortened, which would improve the low frequency characteristics.
In the second prior art Schottky barrier diode, however, since the path of the current adjacent to the surface of the nxe2x88x92 -type GaAs contact layer is still close thereto, the current is still affected strongly by the surface level of the n+ -type GaAs contact layer. As a result, the low frequency noise characteristics of the Schottky barrier diode still deteriorates.
It is an object of the present invention to provide a semiconductor device such as a diode and its manufacturing method capable of reducing the low frequency noise.
Another object is to provide such a semiconductor device incorporating a heterojunction field effect transistor and a heterojunction bipolar transistor and its manufacturing method.
According to the present invention, in a semiconductor device, a first semiconductor layer is formed on a semiconductor substrate. A second semiconductor layer is formed on a part of the first semiconductor layer, and a third semiconductor layer is formed on a part of the second semiconductor layer. A first electrode is formed on the third semiconductor layer, and a second electrode is formed on the first semiconductor layer in contact with the second semiconductor layer and apart from said the semiconductor layer, thus forming a diode.
Thus, the current path is distant from the surface level of the second semiconductor layer, to improve the low frequency noise characteristics.
Also, the cathode electrode is buried in the first semiconductor layer so that the current path is further distant from the surface level of the second semiconductor layer, to further improve the low frequency noise characteristics.